Passengers on Frontier Airlines Flight 787 were startled when the oxygen masks dropped as the airplane was cruising above the Rocky Mountains at 36,000 feet last month. But just how confused they were by an apparent shortage of oxygen masks is just becoming clear from a story reported by Rick Sallinger of the CBS television station in Denver.

As the pilots began a quick descent and a return to the airport in Denver that day, passenger Kevin McClung noticed that not everyone had oxygen masks. “All of the masks did not deploy,” he told Sallinger. “There are two rows that were ahead of me that did not have masks.”

Photo courtesy CBS – 4 TV Denver

Further, McClung said while his wife’s mask was providing her with a stream of oxygen-dense air, his was not working at all and he thought others were having the same trouble.

Photos and a video show a man without a mask struggling with the air vent above his head. These images are being reviewed by the Federal Aviation Administration to determine if Frontier’s oxygen system was defective, Sallinger said.

Peter Kowalchuk, a spokesman for the airline told Sallinger there were no problems with the emergency oxygen system on the Airbus A319 saying, “If all the masks dropped, the only way that there could be unused masks or people without a mask is if there was a mask that was unused, because somebody used the wrong mask and we believe that is what happened.” Well if Frontier can follow that, good for them. As for me, say what Mr. Kowalchuk?

Several years ago I wrote a lengthy article about issues with hypoxia (If you’ve got an hour to spend, be my guest.) Here’s the condensed version: You can quibble all you like about how long it takes to get really sick when an airplane loses pressurization but you can take it to the bank that there’s an immediate diminution of cognitive skills; judgment and comprehension. Since we’re all presumably breathing at ground level now, here’s a quick quiz. How important is it that emergency oxygen masks be easy to find and ready to don? Answer: Pretty darn important.

Whether the McClungs were confused about the number and serviceability of the oxygen masks because they were already feeling the effects of oxygen deprivation, their story is valuable because it reveals potential problems. Is the deployment of the masks confusing? Are the overhead oxygen compartments likely to create disputes among passengers who cannot tell which masks go to which seats?Don’t think decompression events are mere customer service blips, requiring re-booking of passengers and a heartfelt apology for the inconvenience. Alarm bells should start ringing because the danger is real.

One hundred and twenty-one people died in the crash of Helios Flight 522 in 2005. In that accident, a Boeing 737 crashed near Athens after the pilots succumbed to hypoxia on ascent and the plane kept flying on autopilot until it ran out of fuel. The passengers died hours earlier having run through the 12-15 minute oxygen supply at their seats.

Another hypoxia related event worth reviewing is the 1996 decompression aboard American Trans Air Flight 406 which you can find here.

The McClungs and everyone else aboard Flight 787 have put Frontier and the A319 through a real-time test run of the emergency oxygen system. How well did it fare? If safety professionals are clear-headed they’ll follow Sallinger’s example and investigate this event further.